High molecular weight linear thermoplastic polyesters, such as poly (ethylene terephthalate and poly(1,4-butylene terephthalate) are well known as film and fiber-formers and they are provided by methods outlined in Whinfield et al. U.S. Pat. No. 2,465,319, and Pengilly, U.S. Pat. No. 3,047,539, and elsewhere.
Polyester resins, such as poly(alkylene terephthalates, isophthalates and mixed iso - and terephthalates), particularly poly(1,4-butylene terephthalate), also provide excellent molding composition because they can be fabricated with moderate stock temperatures, low mold temperatures and rapid cycle times. Because of their unusual combination of properties, these resins are superior in chemical resistance, thermal stability and product appearance (they have a smooth, glossy finish). Such resins also have superior strength, stiffness, low friction and wear properties and good resistance to brittle fracture. The polyester resins can also be provided in reinforced and flame retardant embodiments.
Solid polyester resins of the type mentioned have found extensive use in various forms of thermoplastic structures. Many different articles of manufacture are produced from polyester compositions by molding extrusion and shaping at higher temperatures because they remain relatively rigid at ordinary room temperature. Polyester fibers are also useful in woven articles and films therefrom are both useful as mechanical supports and as barriers and also they have useful protective coating applications. Although the thermoplastic molding extruded, extrusion blown, injection blown, and coating compositions have the outstanding properties mentioned above, they unfortunately are prone to attack by exposure to light, e.g., UV light. Deterioration caused by UV light which leads to discoloration, embrittlement, and especially loss of physical properties such as tensile strength, tensile elongation and impact strength.
It has now been found that surprisingly stable compositions of polyester resins, with desirable retention of color and physical properties after exposure to UV light are produced when there is admixed therewith a stabilizing amount of a hydroxybenzotriazole ultraviolet light absorber stabilizer.